Ethylene glycol (EG) or ethylene glycol monomethyl ether (EGMME) was administered by gavage to both sexes of B6C3F1 mice for 4 consecutive days at total doses of 200, 400, and 1000 mg/kg body weight. Bone marrow parameters were examined on days 1, 5, and 14 after there final treatment. Exposure to EG produced hypocellularity and suppression of granulocyte-macrophage progenitor (CFU-C) colony formation in both sexes on days 1 and 5 postexposure. Values returned to normal by dy 14 in the female mice but not in the males. Erythropoiesis, as measured by 59Fe incorporation and quantitation of erythroid precursors in culture (CFU-E), revealed no effect in female mice and affected male mice at the high dose only. In contrast, EGMME exposure in female mice resulted in inhibition of erythropoiesis. There was also a pronounced effect on white blood cells with decreased peripheral counts, and decreases in the number of CFU-C's cultured from marrow cells. The effect of EGMME has also seen at the lower dose levels and was sustained through the 14-day evaluation period. In addition, EGMME caused a 20% decrease in testicular weight, which was shown microscopically to be a segmented degeneration of seminiferous tubules, an effect not found with EG. This study demonstrates that EGMME is more myelotoxic in mice than EG and that pancytopenia is more pronounced in males, while erythropoiesis is more affected in females. These results were accepted for publication in J. Environ. Path. Toxicol. Oncol., 1988 (In press).